1. Field of the Invention
The present invention relates to magnetic disk drives. More specifically, it relates to a method which reduces vibration and acoustic noise, and provides greater damping of mechanical resonances, in disk drives. The invention also combines advantageous features in a very small form factor made possible by a novel mechanical and electronics design.
2. Related Art
As magnetic disk drives become smaller, and are used in more diverse environments, the need for quietness becomes more apparent. Noise arises from the rotating spindle motor and the disks attached to its hub, and also from the actuator that supports the read/write heads when a positioning operation is being performed. While these are the sources of acoustic noise in the typical disk drive, amplification can be caused by the mechanical base and cover. In fact, the latter elements may substantially add to the noise as a result of their own resonance characteristics.
Furthermore, independent of acoustic noise, mechanical resonances associated with the components of a disk drive, particularly the actuator, can ultimately cause errors to arise in head-to-track positioning accuracy, thus limiting data recording densities. Also, they can compromise the control of the actuator during track to track positioning operation, increasing the average seek time and so reducing performance.
Known methods of reduction of the negative effects associated with disk drive mechanical resonances have generally followed the pattern of attempting to make all components sufficiently stiff so that their resonant frequencies are made as high as possible, thus allowing the bandwidth of the positioning system to increase in order to improve track following capability and to allow faster seeks. Although this appears to be a sensible procedure, it often suffers from the problem that, although the resonance frequency is increased, the mechanical `gain` or `Q` at resonance also increases, thus tending to reduce the bandwidth improvement that might otherwise be expected. Reducing this gain by, for example, change of geometry or use of composite materials or fastening methods can become difficult and expensive.
Therefore, it is desirable to provide a disk drive which economically and simply includes effective damping of resonances of mechanical components so as to allow a higher degree of positioner accuracy (and thus higher performance), and, at the same time, minimize acoustic noise.
The features of low acoustic noise, damping and simplicity of head parking are especially desirable in disk drives subject to portable applications. Portability itself has its own requirements and objectives. In the computer world, specific designs for portability began in the early 1980's with personal computers weighing around 30 lbs. and supplied with carrying handles. These were more accurately described as `luggable` rather than `transportable`. This style of portable computer has since evolved into second generation `laptop` machines, weighing and measuring considerably less. In parallel with these size-reduction trends in the computer world, the rigid disk drive industry has witnessed its own miniaturization over the last twenty years, from approximate disk diameters of 28" in the 1960's, to 14" and 8" in the 1970's, to 5.25" and 3.5" in the 1980's. These trends in disk drive form factors have been matched by complementary improvements in data storage densities, performance, power requirements and price. The increasing sophistication, availability and universality of popular software during the last few years has fueled the requirement for versatile, high-performance personal computers and driven the hardware developments in the industry. Taking all of those trends together, the growing demand for laptop computers requires a matching availability of small, light-weight, high-performance hard disk drives with data storage capability equivalent to that obtained on drives designed for desktop computers.
There is a demand, therefore, for a small disk drive with typically 40 Megabyte storage capacity suitable for use in very small computer systems, such as laptops, or other systems requiring off-line memory, and with the associated features of quietness, ruggedness and high performance.